Rotating electrical machines

ABSTRACT

A torsional vibration damper is integrated into a rotating electrical machine. A rotatable assembly of the electrical machine includes a rotor core pack having a first end and a second end, The integrated torsional vibration damper consists of a torsional elastic coupling and a torsional elastic damper and provides mechanical damping. The integrated torsional vibration damper is mounted to the rotatable shaft of the electrical machine by a flange. The rotor core pack is mounted at the first end to the integrated torsional vibration damper by suitable structure members such as a mounting flange and is not fixedly mounted directly to the rotatable shaft. In the case where the rotor core pack is cooled by circulating coolant fluid (e.g. MIDEL) then the integrated torsional vibration damper may be a viscous damper that uses the coolant fluid as a viscous working, fluid.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 12,701,842, filedFeb. 8, 2010, entitled ROTATING ELECTRICAL MACHINES, Which applicationclaims priority to European Patent Application No 0.9001871.4 filed Feb.11 , 2009.

FIELD OF THE INVENTION

The invention relates to rotating electrical machines such as motors andgenerators.

BACKGROUND OF THE INVENTION

Torsional vibration dampers (TVDs) are commonly used to providemechanical damping in physically large generator sets where a torque isapplied to the rotatable shaft of an electrical machine b an externaldevice (prime mover) such as a diesel engine or turbine, for example.Such TVDs are used to prevent the build up of dangerous torsionalvibration levels in the rotatable shaft of the electrical machine duringstart-up, shut-down and the normal operation of the generator set.

A stand-alone TVD includes a primary member that is driven by an outputshaft of the prime mover and a secondary member that applies a torque tothe rotatable shaft of the electrical machine. The primary and secondarymembers are elastically connected together by suitable spring sets sothat the torque that is applied to the primary member by the outputshaft of the prime mover is transferred through the spring sets to thesecondary member. Buffers are often provided within the TVD to restrictthe relative rotational movement between the primary and secondarymembers and hence prevent overloading and excessive deflection of thespring sets. Such conventional stand-alone TVDs are physically large,expensive to manufacture and install and add significantly to theoverall length of the generator set. They can also suffer frommisalignment problems.

in the case where the stand-alone TVD is a viscous damper then dampingchambers formed in the body of the secondary member are filled with aviscous working fluid, typically engine oil that is circulated from theprime mover. The damping chambers are connected together by narrowpassageways. Relative rotational movement between the primary andsecondary members of the TVD forces the viscous working fluid throughthe passageways between the damping chambers and past the ends of thespring sets (e.g. leaf springs) to dampen torsional vibrations. Theengine oil has a high operating temperature (about 80° C.) and oftencontains contaminant particles that can cause blockages, increase wearand reduce the reliability of the TVD.

SUMMARY OF THE INVENTION

The present invention improves on the known use of conventionalstand-alone torsional vibration dampers (TVDs) by effectivelyintegrating a TVD that provides mechanical damping within a rotatingelectrical machine. This results in a generator set or motor set that issignificantly more physically compact and hence cheaper and easier toinstall. Other technical advantages arising from the integration of theTVD within the rotating electrical machine (e.g. performanceoptimisation arising from improved control of the mechanical dampingprovided by the TVD) are also discussed in more detail below.

More particularly, the present invention provides a rotating electricalmachine (e.g. a motor or generator) comprising: a rotatable shaft, arotor assembly (e.g. a rotor core pack) concentric with the rotatableshaft and having a first end and a second end, a rotatable shaft, and aviscous nip that employs a viscous working fluid to provide mechanicaldamping, the TVD being mounted to the rotatable shaft, wherein the rotorassembly is mounted at the first end to the torsional vibration damperdevice, and is not fixedly mounted directly to the rotatable shaft butis concentric with it.

It would be normal for a rotor core pack to be made of a series oflaminations which are pressed together and shrunk onto the rotatableshaft. The laminations are typically formed from sheets of electricalgrade steel with the laminations having an appropriate insulatingsubstance e.g. a varnish, resin or other appropriate (organic orinorganic) compound applied thereto. In an operation to assemble such arotor core pack the laminations are typically placed on a mandrel,pressed together at a suitably high pressure and then heated up andshrunk directly onto a pre-machined rotatable shaft. In the presentinvention, there is no need for such an assembly operation since therotor assembly is specifically designed not to be fixedly mounted orsecured directly to the rotatable shaft. Instead at least one end of apre-formed rotor core pack is mounted to the TVD using suitablestructural members.

The rotor assembly provides a rotating magnetic field and this can begenerated by permanent magnets, superconducting windings with a suitableexcitation power supply or conventional windings with slip rings orbrushless excitation power supply, for example.

The rotor assembly is preferably mounted for rotation relative to astator assembly. A stator winding may be received in slots provided in asurface of the stator assembly in a conventional manner.

In an embodiment where only a single TVD is provided at one end of therotor assembly then a bearing is preferably provided between the rotorassembly and the rotatable shaft. Any suitable bearing can be used (e.g.roller, plan, polymer or composite bearings) and is preferably locatedaxially between the rotor assembly and the rotatable shaft. The bearingmay allow relative torsional rotation between the rotor assembly and therotatable shaft and supports the rotor assembly in the radial and/oraxial direction(s). Although the rotor assembly is supported by thebearing, it will be readily appreciated that the rotor assembly is stillnot fixedly mounted or secured directly to the rotatable shaft. Torqueis therefore transferred from the rotatable shaft to the rotor assemblyby means of the TVD and the structural members.

In an alternative “fully-floating” embodiment then a second TVD forproviding mechanical damping is mounted to the rotatable shaft and therotor assembly is mounted at the second end to the second TVD. In otherwords, the rotor assembly is mounted at both ends to the rotor assemblyby a TVD. The TVDs can have the same or different construction dependingon the circumstances. However, if the TVDs have a different constructionthen care must be taken to ensure that the rotor assembly remainsproperly balanced and aligned during start-up, shut-down and normaloperation of the electrical machine.

The first end of the rotor assembly is preferably at the driven ordriving end (DE) of the electrical machine. This is because it willnormally be most useful in the embodiment where only a single TVD isprovided for the TVD to be located between the driving shaft of theprime mover and the rotatable shaft (in the case of a generator set) orbetween the rotatable shaft and a driven load (in the case of a motorset). However, in some embodiments it may be possible for the first endof the rotor assembly to be at the non-driven or non-driving end (NDE)of the electrical machine.

The TVD will employ a viscous working fluid. If the rotating, electricalmachine is air-cooled then the viscous working fluid can be engine oilcirculated from the prime mover of a generator set, for example. Theengine oil can be filtered to remove any contaminant particles beforebeing provided to the TVD. However, if the rotatable assembly has acoolant circuit through which a coolant fluid is circulated for coolingthe rotor assembly (and/or the stator) then it is generally preferredthat the viscous working fluid is the coolant fluid. The coolant circuitwill preferably include means for cooling and filtering the coolantfluid. An example of a suitable coolant fluid is MIDEL and itsequivalents, which is a proprietary transformer insulating fluid. Theuse of the coolant fluid as the viscous working fluid for the TVD isconsidered to be advantageous because of its lower operating temperature(about 40° C. as opposed to about 80° C. for engine oil) and the factthat it does not contain contaminant particles. The absence of anycontaminant particles will reduce the amount wear in the TVD andincrease its reliability. It has also been noted that MIDEL inparticular has a significantly higher viscosity when it is cold andtherefore provides enhanced damping during star as the electricalmachine passes through various torsional resonances.

The mechanical damping provided by the TVD may be used in conjunctionwith any electrical damping of the rotor assembly.

The TVD may consist of a damper having a primary member adapted to bemounted to the rotatable shaft and a secondary member elasticallyconnected to the primary member by one or more spring sets and adaptedto be mounted to the first end of the rotor assembly. The primary memberof the damper can be further adapted to be mounted to a driving shaft ofa prime mover or a driven load.

The TVD may further consist of a coupling having a primary memberadapted to be mounted to a driving shaft of a prime mover or a drivenload and a secondary member elastically connected to the primary memberby one or more spring sets. In this case, the primary member of thedamper is further adapted to be mounted to the secondary member of thecoupling.

The driving shaft of the prime mover may be the crankshaft of a dieselengine or the output shaft of a turbine, for example.

A rotating electrical machine with an integrated viscous TVD can be usedas part of a generator set where a prime mover is adapted to apply atorque to the rotatable shaft of the electrical machine by means of theTVD. In a fully coupled embodiment using a single bearing rotor assemblythen it may be possible to completely omit the engine flywheel and theengine base frame. Such an embodiment would require the electricalmachine frame to match the rear face of block (RFOB) and supporting baseframe of the prime mover. The TVD can be mounted to the rotatable shaftof the electrical machine and drive the rotor core pack by means ofsuitable structural members. The electrical machine may have a singlebearing situated at the non-driven end of the rotatable shaft and abearing associated with the prime mover would withstand axial and radialforces to provide proper axial location for the rotatable shaft. Theelectrical machine may also have bearings at both the driven andnon-driven ends of the rotatable shaft.

A rotating electrical machine with an integrated viscous TVD can also beused as part of a motor set where a driven load is adapted to receive atorque from the rotatable shaft of the electrical machine by means ofthe TVD. Such a motor set may be useful for applications with hightransients like steel or cement mills or where a very smooth drive isrequired (e.g. quiet marine propulsion).

The present invention further provides a method of controlling a viscousTVD mounted to a rotatable shaft of a rotating electrical machine, themethod comprising the step of controlling the flow of viscous workingfluid within the TVD to alter the level of damping that is applied tothe rotatable shaft. The flow rate of viscous working fluid within theTVD, and in particular through the damping chambers and connectingpassageways past any spring sets, can be altered by using any suitableflow restriction valves (which may be located internally or externallyof the electrical machine), control orifices or actuators employingelectronic or mechanical control. For example, flow restriction valvescan be controlled electronically by a damping controller that may formpart of, or be integrated with, a prime mover controller or electricalmachine controller that controls the overall operation of the primemover or electrical machine, respectively. The flow restriction valvescan also be controlled mechanically using thermostatic, centrifugal,pressure and surge controllers.

Controlling the level of damping that is applied to the rotatable shaftby the TVD is expected to be particularly advantageous during transientevents such as start-up and shut-down of the electrical machine. Forexample, a high level of damping can be applied by the TVD duringstart-up and shut-down and a low level of damping can be applied duringnormal operation of the electrical machine, or at times when a highlevel of damping is not expected to be needed. Moving from a high flowrate of viscous working fluid to a low flow rate will result in a changein the level of damping from low damping to high damping or vice versa.Flow restriction valves can be opened to provide a high flow rate ofviscous working fluid during normal operating conditions and hence lowlevel damping. Similarly, flow restriction valves can be closed asrequired to provide a low flow rate of viscous working fluid and hencehigh level damping. It will be readily appreciated that any particularflow rate can be selected by opening or closing the flow restrictionvalves to provide a particular damping level.

Simple damping control may be based on the operating characteristics ofthe electrical machine (e.g. speed or load characteristics) and/or anyassociated machinery. More advanced active damping control may employmodel-based algorithms or adaptive-closed loop control, for example.

The frequency response of the rotatable shaft can be altered bycontrolling the flow of viscous working fluid within the TVD and/orusing the TVD structure as a tuned mass damper (sometimes called anactive mass damper). This enables the dynamic structural response of therotatable shaft to be altered to control critical speed frequencieswhich cause high vibration levels and hence machine fatigue. To form atimed mass damper the TVD is preferably mounted to the rotatable shaftof the electrical machine b a suitable spring and damper mechanism wherethe spring rate and the mass of the TVD are chosen to match one or moreof the critical speed frequencies. Damping between the TVD and therotatable shaft would be provided to restrict the response magnitude.

The radial stiffness of the TVD and damping rates will be chosen tomatch the TVD supported mass and critical frequencies of the rotatableshaft, thus providing the correct dynamic response to reduce thevibrations in the rotatable shaft. A suitable stiffness can be providedby using a suitable radial spring design, such as an elastomeric design,a cantilever spring or a combination of both.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described, withreference to the accompanying drawings, in which:

FIGS. 1 to 3 are cross sectional views of a known torsional vibrationcoupling;

FIGS. 4 to 6 are cross sectional views of a known torsional vibrationdamper;

FIG. 7 is a cross sectional view of a torsional vibration damper (TVD)integrated with a rotating electrical machine in accordance with thepresent invention; and

FIG. 8 is a cross sectional view of the integrated TVD and rotatingelectrical machine of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 to 3, a known torsional elastic coupling ofthe type supplied by Geislinger GmbH of Hallwanger Landesstrasse 3,A-5300 Hallwang/Salzburg, Austria (“Geislinger”) includes a primarymember 2 and a secondary member 4 that are elastically connectedtogether by spring packs. The primary member 2 includes a flange part 6with a series of circumferentially spaced openings 8 that enable it tobe mechanically secured to the crankshaft of a diesel engine, forexample.

The secondary member 4 consists of an intermediate part 10 that islocated between a pair of end plates 12 a, 12 b and a radially outerclamping ring 14. A series of circumferentially-spaced steel springpacks 16 (e.g. leaf springs) are located in damping chambers 18 providedthe intermediate pan 12. The spring packs 16 are clamped by theintermediate part 10 at their radially outer ends and their radiallyinner ends are located in carefully machined grooves or slots (notshown) provided in the primary member 2. The damping chambers 18 arefilled with viscous working fluid, typically engine oil that iscirculated from the diesel engine. The damping chambers 18 are connectedtogether by narrow passageways that are located adjacent the outersurface of the primary member 2. Relative movement between the primaryand secondary members 2, 4 causes the spring packs 16 to bend and forcesthe viscous working fluid from one damping chamber to another to dampentorsional vibrations.

With reference to FIGS. 4 to 6, a known torsional elastic damper of thetype supplied by Geislinger includes a primary member 20 and a secondarymember 22 that are elastically connected together by spring packs.Although the damper and the coupling have different applications, theyhave a similar design. One difference is that the primary member 20 ofthe damper is adapted to be mechanically secured to either input oroutput components. The primary member 20 includes a series ofcircumferentially spaced openings 24 that enable it to be mechanicallysecured to the secondary member 4 of the coupling or directly to thecrankshaft of a diesel engine, for example, in a situation where thedamper is used in isolation.

The secondary member 22 consists of an intermediate part 26 that islocated between a pair of end plates 28 a, 28 h and a radially outerclamping ring 30. A series of circumferentially-spaced steel springpacks 32 (e.g. leaf springs) are located in damping chambers 34 providedthe intermediate part 26. The spring packs 12 are clamped by theintermediate part 26 at their radially outer ends and their radiallyinner ends are located in carefully machined grooves or slots (notshown) provided in the primary member 20. The damping chambers 34 arefilled with viscous working fluid, typically engine oil that iscirculated from the diesel engine. The damping chambers 34 are connectedtogether by narrow passageways that are located adjacent the outersurface of the primary member 20. Relative movement between the primaryand secondary members 20, 22 causes the spring packs 32 to bend andforces the viscous working fluid from one damping chamber to another todampen torsional vibrations.

In both cases, the damping is determined by the passageways whichconnect the damping chambers.

In a known arrangement, the torsional elastic coupling and damper may beused in combination and mounted between the crankshaft of a dieselengine, for example, and the rotatable shaft of a rotating electricalmachine. More particularly, the flange part 6 of the primary member 2 ofthe coupling is mechanically secured to the crankshaft and the secondarymember 4 of the coupling is mechanically secured to the primary member20 of the damper. The primary member 20 of the damper is mechanicallysecured to the driven end of the rotatable shaft by means of a flange.Torque from the crankshaft is transferred to the driven end of therotatable shaft by means of the coupling and damper, which both serve todampen any torsional vibrations in the rotatable shaft. The secondarymember 22 of the damper is not mechanically secured to any othercomponent and acts as a force/torque transfer mechanism to the springsets.

FIGS. 7 and 8 show how a torsional elastic coupling and damper can beintegrated into a rotating electrical machine in accordance with thepresent invention.

A generator 100 consists of a stator assembly 102, a rotor assembly 104(e.g. a rotor core pack) and a rotatable shaft 106. The rotatable shaft106 is supported at its non-driven end by a bearing 108.

A bearing 110 is located between the rotor assembly 104 and therotatable shaft 106 and supports the rotor assembly 104 in the radialand axial directions. It will be readily appreciated that the rotorassembly 104 is not fixedly mounted to the rotatable shaft 106 and notorque is transferred directly from the rotatable shaft to the rotorassembly. The bearing 110 allows relative torsional rotation between therotor assembly 104 and the rotatable shaft 106. The rotor assembly 104is concentric with the rotatable shaft 106 and is mounted for rotationwithin the stator assembly 102.

An integrated torsional vibration damper (TVD) 200 consists of atorsional elastic coupling 202 of the type shown in FIGS. 1 to 3 and atorsional elastic damper 204 of the type shown in FIGS. 4 to 6.

The flange part 6 of the primary member 2 of the coupling 202 ismechanically secured to the crankshaft (not shown) of a diesel engine,for example. The secondary member 4 of the coupling 202 is mechanicallysecured to the primary member 20 of the damper 204.

The primary member 20 of the damper 204 is mechanically secured to thedriven end of the rotatable shaft 102 by means of a flange 112. Torquefrom the crankshaft (not shown) of the diesel engine is transferred tothe driven end of the rotatable shaft 106 by means of the elasticallyconnected primary and secondary members 2, 4 of the coupling 202, theprimary member 20 of the damper 204 and the flange 112. Torsionalvibrations between the crankshaft (not shown) of the diesel engine andthe rotatable shaft 106 are therefore damped by the coupling 202.

The secondary member 22 of the damper 204 is mechanically secured to anend of the rotor assembly 102 by means of a flange 114. However, in somearrangements the flange 114 can be omitted such that the rotor assembly102 is connected directly to the secondary member 22 of the damper 204.Torque from the crankshaft (not shown) of the diesel engine istransferred to the driven end of the rotor assembly 104 by means of theelastically connected primary and secondary members 2, 4 of thecoupling, the elastically connected primary and secondary members 20, 22and the flange 114. Torsional vibrations between the rotatable shaft 106and the rotor assembly 104 are therefore damped by the damper 204.

A coolant fluid such as MIDEL and its equivalents is circulated along acoolant circuit provided by passageways 116 a, 116 b in the rotatableshaft 106. The coolant fluid is supplied to, and removed from, therotatable shaft 106 through a collar assembly 118. At the driven end ofthe rotatable shaft 106 the coolant fluid is supplied into the coupling202 and damper 204 of the integrated TVD 200 through openings providedin the flange 112. The coolant fluid is therefore circulated through thedamping chambers 18, 34 provided in the intermediate parts 12, 26 of thecoupling and damper, respectively, where it acts as the viscous workingfluid for the integrated TVD 200. It is advantageous to use coolantfluid instead of engine oil circulated from the diesel engine because ithas a lower operating temperature (about 40° C. as opposed to about 80°C. for engine oil) and it does not contain contaminant particles. Theabsence of any contaminant particles will reduce the amount wear in theintegrated torsional vibration assembly and increase its reliability.However, if the generator 100 is air-cooled then engine oil can becirculated from the diesel engine in the usual way.

The flow of coolant fluid (or engine oil) within the integrated TVD 200can be controlled to change the level of damping that is applied to therotatable shaft 106 by the integrated TVD. This can be achieved usingany suitable flow restriction valves, control orifices or actuators (notshown) employing mechanical or electronic control. The flow restrictionvalves can be located within the integrated TVD in the case where therotor assembly is cooled by a circulating coolant fluid such as MIDELand either internally or externally of the generator where the rotorassembly is air-cooled. Internally fitted flow restriction valves willtypically be controlled mechanically (e.g. using thermostatic,centrifugal speed and pressure control methods), but they can also becontrolled electronically by providing control signals to the flowrestriction valves using either wireless or wired arrangements (e.g.using slip rings). Externally fitted flow restriction valves willtypically be controlled electronically by providing control signals froma diesel engine controller or generator controller as appropriate.

By adding controlled radial spring stiffness and damping rates theintegrated TVD 200 can be used as a tuned mass damper to control thecritical speed frequencies of the rotatable shaft.

Although the integrated TVD 200 has been explained above in the contextof a generator, it will be readily appreciated that the rotatingelectrical machine can be a motor such that the flange 6 of the coupling202 is mechanically secured to a driven load such as the propeller shaftof a marine propulsion motor, for example.

What is claimed is:
 1. A method of controlling a viscous torsionalvibration damper mounted to the rotatable shaft of a rotating electricalmachine, the method comprising the step of controlling the flow ofviscous working fluid through the viscous torsional vibration damper toalter the level of damping that is applied to the rotatable shaft.